Some insect larvae, such as the larvae of the black soldier fly (BSF; Hermetia illucens) are particularly well suited to converting a wide variety of organic materials into alternative products. The organic material may for example include commercial or residential waste products, such as fruit and vegetable matter, coffee pulp, meat, fish, bread, grains, or manures. The value-added products of BSF bioconversion may for example, include livestock feed or feed ingredients (for terrestrial or aquatic animals), pet food, food stuffs for human consumption, or plant growth media. To take advantage of this natural aptitude for bioconversion, various techniques for utilizing BSFs in bioconversion systems have been described, see: WO2013166590, WO2012100077 and WO2010002188,
There are a number of characteristics of BSFs that have been considered advantageous in alternative bioconversion systems. BSF larvae and prepupae are high in protein and fatty acid content and exhibit natural behaviors that can form the basis of self-harvesting systems. BSF adults are not generally considered to be disease vectors. BSF larvae may demonstrate anti-pathogenic qualities (Erickson, et al. 2004; Liu, et al. 2008). Finally, BSF larvae may be cultured so as to produce stable colonies, at least in part because they deter colonization from other insect species (Bradley and Sheppard, 1984) and can survive in a variety of environmental conditions.
As a member of the Family Stratiomyidae, the BSF goes through full metamorphosis during its lifespan. This includes the egg, larval, pupae and adult life cycle stages. Larvae will hatch from the egg stage after 48-72 hours and go through five instars (larval stages) before reaching the pupae stage. The first instar (L1) will molt into the second instar (L2) within 4-5 days and generally reach the pupae stage within a further 12-30 days, depending on temperature, humidity, type of feed, quantity of feed, frequency of feeding, mixture of feed ingredients, moisture of feed, starter diet, finishing diet and consistency of feed. Between the fifth instar (L5) and the pupae stage is the prepupae stage, where BSF larvae generally seek a drier environment to complete the metamorphosis stage of its life cycle. The pupae stage generally lasts 7-20 days, depending on factors such as, for example, movement, proximity to other moving pupae, level of light, temperature and humidity, following which the adult fly will emerge. Adult BSFs mate and gravid female BSFs will lay eggs (i.e., “oviposit”) for the next generation. The life span of an adult BSF is generally 6-15 days, depending on humidity (e.g., 50-90%) and/or temperature (e.g., 22-35° C.) and stored energy, such as quantities and profiles of protein and fat. The foregoing timelines associated with the typical BSF life cycle are necessarily approximations, with variations that generally depend on environmental conditions and food supply. For example, it has been reported that limited food supply can extend the larval period to 4 months (Furman et al., 1959).
Under appropriate conditions, gravid female BSF adults will oviposit eggs approximately 24-72 hours after mating. Eggs are generally oviposited in tight, narrow spaces, such as blocks of cardboard with flutes oriented in any direction. Females are typically attracted to oviposition sites with pungent odours, or other biochemical signals derived from BSF eggs or gravid BSF females, as this usually indicates a potential food source for BSF offspring. BSF adults require specific environmental conditions to induce mating behaviors, including particular ranges of light, space, temperature and humidity. BSF will survive and mate at temperatures between 22° C. and 35° C. and humidity levels between 30% and 90%. For example, BSF will survive and mate at an ambient air temperature of approximately 25° C.-30° C. with a relative humidity of approximately 60-80%. It has been reported that a BSF colony can be maintained at 22° C. (Tomberlin and Sheppard, 2002) and that the upper limit for optimal development of the BSF is between 30-36° C. (Tomberlin et al., 2009). A study measuring BSF mating and oviposition reported that 80% percent of egg clutches were deposited when humidity exceeded 60% (Tomberlin and Sheppard, 2002).